As means for improving properties and, specifically, gas-barrier property of various plastic base materials, there has been known an art of forming an inorganic barrier layer of a silicon oxide or the like by vacuum evaporation on the surfaces of the plastic base materials (patent document 1).
In a variety of kinds of electronic devices that have been developed and put into practice in recent years, such as organic electroluminescent (organic EL) devices, solar cells, touch panels, e-papers and the like, that must avoid leakage of the electric charges, it is a requirement to impart a high degree of water-barrier property to the plastic base materials forming the circuit boards or to the films sealing the circuit boards. However, the inorganic barrier layer formed as described above is not capable of meeting the requirement for attaining water-barrier property of a high level. Therefore, a variety of proposals have been made for improving water-barrier property.
A patent document 2, for example, proposes a gas-barrier laminate comprising an inorganic barrier layer formed on the surface of a plastic base material, and a sealing layer formed on the inorganic barrier layer, the sealing layer being dispersed with nanoparticles of a metal oxide or carbon nanotubes as a hygroscopic agent.
A patent document 3 proposes a gas-barrier laminate (film) comprising an inorganic barrier layer, an organic layer and a water-trapping layer formed on a base film, the water-trapping layer being formed of a hygroscopic polymer (concretely, a polyamide) or being formed by dispersing a hygroscopic material such as silica gel or aluminum oxide in a high molecular binder such as a resin that can be cured with electron rays or ultraviolet rays.
Further, a patent document 4 proposes a gas-barrier laminate comprising a gas-barrier film and a hygroscopic layer formed by vacuum evaporation on the surface of a plastic base material, the hygroscopic layer containing an alkylene oxide, acrylate nanoparticles or an organometal complex.
However, the gas-barrier laminates proposed by the above patent documents 2 to 4 are not still capable of attaining high degrees of water-barrier property. To attain a super-barrier property against water such that a water vapor permeability is, for example, 10−5 g/m2/day or less, it becomes necessary to employ a layer structure that includes many layers (hygroscopic layers or sealing layers) for absorbing moisture. As a result, a lot of laborious work is needed for forming a multi-layered structure causing a decrease in the productivity. Therefore, it has been desired to further improve water-barrier properties. Besides, there still remains a problem in that upon absorbing the moisture, the layers (hygroscopic layers or sealing layers) for absorbing moisture undergo swelling and lose dimensional stability. Therefore, it has been desired to provide a hygroscopic layer that is capable of exhibiting excellent hygroscopic property over extended periods of time for also realizing super-barrier property using the layers of a number as small as possible.
To meet the above requirements, the present applicant has previously proposed a gas-barrier laminate having a water-trapping layer in which a specific hygroscopic agent was dispersed in the matrix of an ionic polymer, the water-trapping layer being formed on an inorganic barrier layer on a plastic base material (JP-A-2013-22253, JP-A-2013-022656 and JP-A-2014-41672). In the gas-barrier laminate proposed here, the water-trapping layer effectively traps water. Therefore, the gas-barrier laminate not only exhibits very excellent water barrier property but also effectively suppresses the water-trapping layer from swelling despite of having absorbed moisture.